1. Field of the Invention
The present invention relates to a data recorder which records and reproduces data sent from, e.g., a computer using a rotary head type digital audio tape recorder (DAT).
2. Description of the Prior Art
In a computer, in order to protect (back-up) data written in a hard disk or the like, these data are transferred to and recorded in a data streamer (data recorder) once a day.
As a conventional data recorder, a 1/4-inch data cartridge type data recorder is often used. However, the data recorder consumes a large amount of a magnetic tape, and has a low data rate in a recording mode. Therefore, a transfer/recording operation is time-consuming. Since the data recorder cannot perform a high-speed search operation, it takes a lot of time to search a starting portion of desired data.
A digital audio tape recorder of a helical scan type using a rotary head which has been recently commercially available, a so-called DAT, is used as a data recorder. When the DAT is used as the data recorder, data from the host computer is converted into data having a DAT format and is then recorded. In the DAT format, two oblique tracks formed during one revolution of two heads having different azimuth angles are given as one frame, and 16-bit pulse code modulated (PCM) audio data is divided by half to provide two 8-bit data, which are interleaved and recorded in units of frames. In addition, sub data is recorded. In this case, as will be described later, a main area for recording PCM data and a sub area for recording sub data are formed on each track. FIG. 1 shows a tape format when a DAT is used as a data recorder.
Referring to FIG. 1, a magnetic tape 17 consists of a magnetic body portion having a total length L.sub.0 (tape length), and transparent leader tape portions 17a and 17b which are connected to respective ends of the magnetic body portion. A leading end of the magnetic body portion is called a BOM (Beginning Of Media), and its ending end is called an EOM (End of Media). An EOT (End Of Tape) representing a pre-end is located at a position distant from the EOM toward the BOM by a length of l.sub.2. A point located at a position distant from the BOM by a length of l.sub.1 is called a BOT (Beginning Of Tape). A variety of data to be described later are recorded after the BOT. An area from the BOM to the BOT is called a device area 17c. The device area 17c is kept blank or a signal for testing an apparatus is recorded in and reproduced from the device area 17c. When a head is present in the device area 17c, a tape cassette is attached/detached or the tape 17 is loaded or unloaded. Note that the length l.sub.1 is, e.g., l.sub.1 =350 .+-.10 mm and that the length l.sub.2 is, e.g., l.sub.2 =500 mm (.apprxeq.2045 frames). A reference area 17d of 35 frames follows the device area 17c to record therein a signal representing the starting portion of data. A system area 17e of 115 frames follows the reference area 17d to record therein history such as the number of read and write opeations, the number of errors and the like. The system area 17e is followed by an area of 23 frames called a vendor group 17f which can record therein desired data. The vendor group 17f is followed by a group area 17g in which there is recorded back-up data sent from a host computer. The group area 17g includes a plurality of groups each having 23 frames. Next to the group area 17g, an EOD (End Of Data) signal is recorded in 300 frames so that, upon reproduction, any data found to be recorded after the EOD is ignored as old data. An area from the BOM to the system area 17e is called a lead-in area, and an area including the vendor group 17f and the group area 17g is called a data area.
When the DAT is employed as the data recorder and data is recorded and reproduced according to the above-mentioned format, the contents of a table must be recorded in the tape 17 in order to know types and positions of data sent from the host computer and recorded in the tape 17. The contents of table include, e.g., a data file name, date on which data is formed, the name of a person who forms the data, brief contents of data and data address. An area in which the contents of table are recorded is called a directory area. The directory area of desired length is typically recorded in a proper position next to the BOT or recorded just before the EOD shown in FIG. 1 according to a predetermined data format.
In this case, however, a special data format for the directory area must be provided, which unavoidably causes software and hardware of the system to be considerably modified. Further, a special command signal must be prepared to make an access between a central processing unit (CPU) and the system. In addition, when the directory area is provided just before the EOD, then it takes plenty of time to read the directory area after the tape cassette is loaded on the DAT. Furthermore, there is a possibility that, during data recording, directory data recorded will be inadvertently erased by a malfunction or the like.